Semiconductor device manufacturers and users share a common concern for the amount of heat dissipated by a semiconductor device. Uncontrolled temperature increases at a semiconductor device P-N junction, i.e., high heat dissipation, may result in the device failing. One technique for measuring the temperature of a P-N junction exploits the relationship between current flowing through a forward biased P-N junction and the applied voltage across the P-N junction. More particularly, the current flowing through a forward biased P-N junction varies in accordance with the applied voltage across the P-N junction, the junction area, and the junction temperature. Thus, the forward voltage drop across a P-N junction, at a constant current, can be calibrated and used as a measure of the junction temperature.
In one approach, a polysilicon temperature sensing diode is formed in a polysilicon layer on a gate oxide region of a metal-oxide-semiconductor (MOSFET) transistor. The temperature of the sensing diode increases in response to an increase in the substrate temperature whereas the forward voltage drop across the sensing diode decreases. A drawback to this technique is the presence of a substantial thermal impedance, resulting from the oxide, between the temperature sensing diode and the semiconductor substrate. Further, the resistance of a polysilicon diode can vary, thereby adding variability to the forward voltage drop across the sensing diode.
Accordingly, it would be advantageous to have a new and novel method and means for sensing the temperature of an insulated gate semiconductor device, wherein the temperature sensing portion is integrated in the same mono-crystalline substrate as the insulated gate semiconductor device.